Method for polishing work and work polishing apparatus

ABSTRACT

The method of the present invention is capable of polishing a high hardness work at high polishing efficiency. The method comprises the steps of: pressing a surface of the work onto a polishing part of a rotating polishing plate; and supplying slurry while performing the pressing step. The method is characterized in that an activated gas, which has been activated by gas discharge, is turned into bubbles and mixed into the slurry.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2014-051394, filed on Mar. 14,2014, and the entire contents of which are incorporated herein byreference.

FIELD

The present invention relates to a method for suitably polishing a workcomposed of a high hardness material, e.g., SiC, and a work polishingapparatus for suitably polishing the same.

BACKGROUND

Flattening substrates is essential for producing semiconductor powerdevices. However, substrates of wide band gap semiconductors composedof, for example, silicon carbide (SiC), gallium nitride (GaN), diamond,are hard and fragile, so it is difficult to efficiently flatten saidsubstrates by mechanical processing.

Patent Document 1 discloses a manner of using slurry including abrasiveparticles and micro-nano bubble water.

Further, Patent Document 2 discloses a polishing method for reducingpolishing defects and polishing works at a high polishing rate, in whicha first processing liquid including abrasive particles and a secondprocessing liquid including electrolytes and micro-nano bubbles havingdiameters of 10 nm-1000 μm are used.

PRIOR ART DOCUMENTS

Patent Document 1: Japanese Laid-open Patent

Publication No. 2009-111094 Patent Document 2: Japanese Laid-open PatentPublication No. 2008-235357

SUMMARY

In the technologies disclosed in Patent Documents 1 and 2, micro-nanobubbles are included in the slurry or the processing liquid so as toimprove polishing rate and reduce polishing defects. However, it isdifficult to polish materials having high hardness and processingresistance, e.g., SiC, diamond, at an efficient polishing rate even bythe technologies disclosed in said patent documents.

The present invention has been performed to solve the above describedproblem of the conventional technologies. Accordingly, it is an objectto provide a method and an apparatus for polishing a work, which arecapable of polishing high hardness materials at high polishingefficiency.

To achieve the object, the present invention has followingconstitutions.

Namely, the polishing method of the present invention comprises thesteps of:

pressing a surface of the work onto a polishing part of a rotatingpolishing plate; and

supplying slurry while performing the pressing step, and

the method is characterized in that an activated gas, which has beenactivated by gas discharge, is turned into bubbles and mixed into theslurry.

In the method, the activated gas may be directly mixed into the slurryin which abrasive particles have been mixed.

In the method, the slurry may be produced by mixing a liquid includingabrasive particles with another liquid including the activated gas.

In the method, another liquid may be water.

In the method, the gas to be activated may be air, oxygen, an inert gas,a fluorine gas or a mixture thereof.

Preferably, the activated gas is a micro activated gas.

The work polishing apparatus of the present invention comprises:

a slurry supplying section;

a polishing plate having a polishing part, onto which a surface of awork is pressed, with supplying slurry, while rotating the polishingplate so as to polish the work;

a gas discharging section for generating an activated gas by gasdischarge; and

a bubble generating section for turning the activated gas, which hasbeen activated by the gas discharging section, into bubbles, and

the activated gas is mixed into the slurry.

In the apparatus, abrasive particles may be mixed into the slurry, andthe bubble generating section may directly mix the bubbles of theactivated gas with the slurry including the abrasive particles.

In the apparatus, the bubble generating section may mix the bubbles ofthe activated gas into another liquid, and the slurry, which has beensupplied from the slurry supplying section and which includes theabrasive particles, may be mixed with another liquid including theactivated gas.

In the apparatus, the gas discharging section and the bubble generatingsection may be constituted by:

-   -   an electrode/gas supplying section being provided in the        polishing plate; and    -   a high-voltage power source for applying high voltage to the        electrode/gas supplying section, and

the bubbles of the activated gas, which have been generated by the gasdischarging section and the bubble generating section, may be mixed intothe slurry, which is supplied onto the polishing plate from the slurrysupplying section.

In the present invention, the work can be highly efficiently polished byinteraction of the mechanical polishing performed by the abrasiveparticles and the chemical polishing performed by the gas, which hasbeen activated by gas discharged. Further, the work is polished by notonly the mechanical polishing but also the chemical polishing, so thework composed of a high hardness material, e.g., SiC, GaN, diamond, canbe suitably polished.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexamples and with reference to the accompanying drawings which are givenby way of illustration only, and thus are not limitative of the presentinvention, and in which:

FIG. 1 is an explanation view showing an outline of the work polishingapparatus of a first embodiment;

FIG. 2 is an explanation view showing an outline of the work polishingapparatus of a second embodiment;

FIG. 3 is an explanation view showing an outline of the work polishingapparatus of a third embodiment; and

FIG. 4 is a graph showing results of experimental examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings. The method of thepresent invention is performed in the apparatus thereof, so the methodand apparatus will be explained together.

FIG. 1 is an explanation view showing an outline of the work polishingapparatus 10 of a first embodiment.

In the first embodiment, a surface of a work W held by a polishing head12 is pressed onto a polishing part 18, which is provided on a rotatingpolishing plate 16, with supplying slurry from a slurry supplyingsection 14, so as to polish the surface of the work W. The presentembodiment is characterized in that an activated gas, which has beenactivated by gas discharge, is turned into bubbles and mixed into theslurry.

The polishing plate 16 is rotated, by a driving mechanism (not shown),about a shaft 20, in a horizontal plane. A surface of the polishingplate 16 acts as a polishing part 18. The polishing cloth composed of,for example, unwoven cloth or a polyurethane resin sheet is adhered onthe polishing part 18. Further, the polishing part 18 may be formed byembedding special particles in the surface of the polishing plate 16.

The work W is held on a bottom surface of the polishing head 12 by, forexample, a double-stick tape or air suction. Various known polishingheads may be employed as the polishing head 12. The polishing head 12can be moved upward and downward, and rotated about a shaft 22 in ahorizontal plane.

The slurry supplying section 14 supplies the slurry, which includesabrasive particles, onto the polishing part 18 of the polishing plate16. The slurry may be selected from various types of known slurryaccording to a material of the work W, etc.

A gas is introduced into a gas discharging section 24 by a pump 25, andthe gas is turned into plasma so as to generate an activated gas. Thegas discharging section 24 turns the gas into plasma by, for example,dielectric-barrier discharge. Note that, the discharging manner of thegas discharging section 24 is not limited to the dielectric-barrierdischarge. The gas may be activated by corona discharge, sparkdischarge, etc. in the gas discharging section 24.

The activating function of the gas discharging section 24 has beenknown. By turning the gas into plasma, radical species, e.g., OHradical, according to gas species are produced and chemically activated,so that oxidizing function, etching function, etc. can be obtained.

Note that, air, oxygen, an inert gas, a fluorine gas or a mixturethereof can be used as the gas species.

A bubble generating section 26 has a known structure.

Water stored in a tank 27 is introduced into the bubble generatingsection 26, and the activated gas 26 generated in the gas dischargingsection 24 is introduced into the bubble generating section 26 via atube 28, so that the activated gas can be mixed into the water as microbubbles. The water including the micro bubbles is returned to the tank27.

The water including the activated gas in the form of micro bubbles issupplied onto the polishing part 18 of the polishing plate 16, via atube 29, by a pump (not shown), and mixed with the slurry includingabrasive particles, which has been supplied from the slurry supplyingsection 14. Water is resupplied to the tank 27 from a water supplyingsection (not shown). Note that, the liquid including the activated gasturned into micro bubbles (the micro activated gas) is not limited towater. For example, electrolyzed water, whose pH value has beenadjusted, may be used instead of water.

In the bubble generating section 26, the gas activated by gas dischargeis turned into micro-nano bubbles. Namely, micro-nano bubble water, inwhich bubbles of micro (μm) level and bubbles of nano (nm) level aremixed, is produced in the bubble generating section 26. The micro-nanobubble water is supplied onto the polishing part 18 of the polishingplate 16 and mixed with the slurry supplied from the slurry supplyingsection 14.

Note that, in the above described embodiment, the gas dischargingsection 24 is separated from the bubble generating section 26, but theboth sections may be combined as one unit (not shown). In this case,generating micro-nano bubbles and gas discharge may be simultaneouslyperformed so as to generate the radical species and micro-nano bubblesin the liquid (see, for example, Japanese Laid-open Patent PublicationNo. 2013-86072). The method and the polishing apparatus in which the gasdischarging section 24 and the bubble generating section 26 are combinedas one unit is also included in the scope of the present invention(claims 1 and 11).

The slurry supplied from the slurry supplying section 14 and themicro-nano bubble water supplied from the tank 27 are mixed, so that themixed slurry can be used for polishing the work W.

The slurry supplied from the slurry supplying section 14 includesabrasive particles, and the abrasive particles are highly uniformlydispersed in the mixed slurry by function of the micro-nano bubbles.Therefore, the work W can be uniformly polished.

The gas, which has been activated by gas discharge, is mixed into themicro-nano bubble water in the form of micro-nano bubbles, so that theactivated gas directly acts on the surface of the work W. Therefore, thesurface of the work W can be oxidized and etched. By the oxidizingfunction and the etching function, the surface of the work W ismetamorphosed, and the metamorphosed layer can be removed by amechanical polishing function of the slurry including abrasiveparticles.

Further, many OH⁻ ions will gather around micro-nano bubbles whenmicro-nano bubbles are electrically charged. When the charged micro-nanobubbles disappear in the state where many OH⁻ ions gather therearound,the oxidizing function and the etching function can be obtained byactivation of OH radical, and superior effects can be obtained, wethink.

In the present embodiment, the work W can be highly efficiently polishedby the interaction of the mechanical polishing action of the abrasiveparticles (the mechanical polishing action, uniformly performed bymicro-nano bubbles) and the chemical polishing action of the, gasactivated by gas discharge (e.g., plasma gas). Further, the oxidizingfunction and the etching function, which are performed by activation ofOH radical when the micro-nano bubbles disappear, are added. Since themechanical polishing and the chemical polishing are performed, highhardness materials, e.g., SiC, GaN, diamond, can be suitably polished.

FIG. 2 is an explanation view showing an outline of the work polishingapparatus 10 of a second embodiment.

The structural elements explained in the first embodiment are assignedthe same symbols, and explanation will be omitted.

In the second embodiment, the slurry including abrasive particles issupplied from the slurry supplying section 14 to the tank 27, and theactivated gas, which has been turned into plasma and micronized (microactivated gas), is directly mixed into the slurry stored in the tank 27.

In the present embodiment too, the work W can be highly efficientlypolished by the interaction of the mechanical polishing action of theabrasive particles (the mechanical polishing action uniformly performedby micro-nano bubbles) and the chemical polishing action of the gasturned into plasma and activated. Further, by performing not only themechanical polishing but also the chemical polishing, high hardnessmaterials, e.g., SiC, GaN, diamond, can be polished. Further, in thepresent embodiment, the slurry may be circulated to reuse.

FIG. 3 is an explanation view showing an outline of the work polishingapparatus 10 of a third embodiment.

The structural elements explained in the first embodiment are assignedthe same symbols, and explanation will be omitted.

In the present embodiment, a porous member 30, which is composed of, forexample, SUS, is provided in the polishing plate 16 as an electrode/gassupplying section which acts as an electrode and a gas supplyingsection. A ceramic plate (an insulation plate) 32 covers the porousmember 30. In the polishing part 18, the adhered polishing cloth coversthe ceramic plate 32. The ceramic plate 32, which faces to the polishinghead 12, has many small holes 33.

The polishing head 12 and the slurry (the slurry supplying section 14)are electrically grounded, and a high-voltage power source 34 isconnected to the porous member 30, which acts as the electrode/gassupplying section, so as to supply high voltage thereto. Further, aprescribed gas is supplied to the porous member 30 from a gas source(not shown).

The work polishing apparatus 10 of the third embodiment has the abovedescribed structure.

In the present embodiment, high voltage is applied from the high-voltagepower source 34 to the porous member 30 with supplying the prescribedgas from the gas source (not shown) to the porous member 30. Then,electric discharge is performed between the porous member 30 and theslurry or the work W, and the gas supplied to the porous member 30 isactivated, discharged from the porous member 30, turned into bubbles,supplied onto the polishing part (polishing cloth) 18 via the smallholes 33 of the ceramic plate 32, and mixed with the slurry, which hasbeen supplied from the slurry supplying section 14 and which includesthe abrasive particles. Therefore, the work W can be suitably polishedas well as the first and second embodiments.

The gas discharging section and the bubble generating section areconstituted by the porous member 30, the high-voltage power source 34,the gas source (not shown), etc.

Note that, in the present embodiment, high voltage is applied to theporous member 30, but high voltage may be applied to the polishing head12 or the slurry supplying section 14.

In each of the above described embodiments, the polishing apparatus isthe one side polishing apparatus, but the present invention can beapplied to a double side polishing apparatus.

Next, experimental examples will be explained.

The polishing apparatus 10 shown in FIG. 1 was used in the experiment.Micro-nano bubble water including a micro activated gas, which hadturned into plasma and activated, was produced, and a work W composed ofa SiC substrate was polished with supplying slurry mixed with themicro-nano bubble water to the polishing cloth (the polishing part 18)of the polishing plate 16.

In the gas discharging section 24, air was flown at a flow rate of 0.3L/min. and turned into plasma by dielectric-barrier discharge at ahigh-frequency voltage of 17 kV so as to produce an activated gas. Thebubble generating section 26 was a micro-nano bubble generating unit ofType AGS2 manufactured by Asupu Co. Ltd. Sizes of most bubbles were25-45 μm, but bubbles of nano level were also included.

The used slurry was DSC0902 produced by Fujimi Inc. The used polishingcloth was SUBA600 manufactured by Nitta Haas Inc.

Experimental results are shown in FIG. 4.

As shown in FIG. 4, a polishing rate of a “polishing liquid including50% of the plasma micro-nano bubble water and 50% of the slurry” wasabout two times higher than that of a “polishing liquid including 50% ofmere micro-nano bubble water and 50% of the slurry”. Note that, thepolishing rate of the “polishing liquid including 50% of the meremicro-nano bubble water and 50% of the slurry” was slightly higher thanthat of the 100% slurry. In case of using a “polishing liquid including50% of pure water and 50% of the slurry”, the slurry was diluted, sopolishing function was seldom obtained as a matter of practice.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alternations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method for polishing a work, comprising thesteps of: pressing a surface of the work onto a polishing part of arotating polishing plate; and supplying slurry while performing thepressing step, the method being characterized in, that an activated gas,which has been activated by gas discharge, is turned into bubbles andmixed into the slurry.
 2. The method according to claim 1, wherein theactivated gas is directly mixed into the slurry in which abrasiveparticles have been mixed.
 3. The method according to claim 1, whereinthe slurry is produced by mixing a liquid including abrasive particleswith another liquid including the activated gas.
 4. The method accordingto claim 3, wherein another liquid is water.
 5. The method according toclaim 1, wherein the gas to be activated is air, oxygen, an inert gas, afluorine gas or a mixture thereof.
 6. The method according to claim 1,wherein the activated gas is a micro activated gas.
 7. The methodaccording to claim 2, wherein the activated gas is a micro activatedgas.
 8. The method according to claim 3, wherein the activated gas is amicro activated gas.
 9. The method according to claim 4, wherein theactivated gas is a micro activated gas.
 10. The method according toclaim 5, wherein the activated gas is a micro activated gas.
 11. A workpolishing apparatus, comprising: a slurry supplying section; a polishingplate having a polishing part, onto which a surface of a work ispressed, with supplying slurry, while rotating the polishing plate so asto polish the work; a gas discharging section for generating anactivated gas by gas discharge; and a bubble generating section forturning the activated gas, which has been activated by the gasdischarging section, into bubbles, wherein the activated gas is mixedinto the slurry.
 12. The work polishing apparatus according to claim 11,wherein abrasive particles are mixed into the slurry, and the bubblegenerating section directly mixes the bubbles of the activated gas withthe slurry including the abrasive particles.
 13. The work polishingapparatus according to claim 11, wherein the bubble generating sectionmixes the bubbles of the activated gas into another liquid, and theslurry, which has been supplied from the slurry supplying section andwhich includes the abrasive particles, is mixed with another liquidincluding the activated gas.
 14. The work polishing apparatus accordingto claim 13, wherein another liquid is water.
 15. The work polishingapparatus according to claim 11, wherein the gas discharging section andthe bubble generating section are constituted by: an electrode/gassupplying section being provided in the polishing plate; and ahigh-voltage power source for applying high voltage to the electrode/gassupplying section, and wherein the bubbles of the activated gas, whichhave been generated by the gas discharging section and the bubblegenerating section, are mixed into the slurry, which is supplied ontothe polishing plate from the slurry supplying section.
 16. The workpolishing apparatus according to claim 11, wherein the gas to beactivated is air, oxygen, an inert gas, a fluorine gas or a mixturethereof.
 17. The work polishing apparatus according to claim 11 whereinthe activated gas is a micro activated gas.
 18. The work polishingapparatus according to claim 12 wherein the activated gas is a microactivated gas.
 19. The work polishing apparatus according to claim 13wherein the activated gas is a micro activated gas.
 20. The workpolishing apparatus according to claim 14 wherein the activated gas is amicro activated gas.
 21. The work polishing apparatus according to claim15 wherein the activated gas is a micro activated gas.
 22. The workpolishing apparatus according to claim 16 wherein the activated gas is amicro activated gas.